PPC Cement | Portland Pozzolana Cement

The Portland Pozzolana Cement is a kind of Blended Cement which is produced by either intergrinding of OPC clinker along with gypsum and pozzolanic materials in certain proportions or grinding the OPC clinker, gypsum and Pozzolanic materials separately and thoroughly blending them in certain proportions.

Pozzolana is a natural or artificial material containing silica in a reactive form. It may be further discussed as siliceous or siliceous and aluminous material which in itself possesses little, or no cementitious properties but will in finely divided form and in the presence of moisture, chemically react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties. It is essential that pozzolana be in a finely divided state as it is only then that silica can combine with calcium hydroxide (liberated by the hydrating Portland cement) in the presence of water to form stable calcium silicates which have cementitious properties. The pozzolanic materials commonly used are:

Volcanic ash

Calcined clay

Fly ash

Silica fumes

The Indian standards for Portland Pozzolana Cement have been issued in two parts based on the type of pozzolanic materials to be used in manufacturing of Portland Pozzolana Cement as given below:

IS 1489 (Part 2) 1991, Portland Pozzolana Cement – specification (Calcined clay based) the quality of flyash or calcined clay to be used in manufacturing of PPC is also specified by BIS in the following standards:

IS 3812 1981 – specification for flyash as pozzolana and admixture IS 1344 1981 – specification for calcined clay pozzolana In view of the availability of good quality fly ash in abundant quantity, the use of calcined clay based pozzolana cement is progressively decreasing. The flyash is a waste product of Thermal power Plant which creates disposal problems at Thermal power plant site. The yearly production of flyash in India is about 70 million tonnes per annum. This would increase in future depending upon the new coal based thermal power plants to be installed in the country. The present utilisation of fly ash in production of blended cement in India is meagre.

Fly ash is the ash precipitated electrostatically from the exhaust fumes of coal fired power station. The fly ash particles are spherical and are generally of higher fineness than cement so that the silica is readily available for reaction. As per IS 3812: 1981 the percentage of silica and alumina should be minimum 70% and maximum loss on ignition 12%. Much superior quality fly ash is available from Indian thermal power plants than specified in IS code.

The Portland Pozzolana Cement makes concrete more impermeable and denser as compared to Ordinary Portland Cement. The long-term strength (90 days and above) of Pozzolana cement is better compared to OPC. The pozzolanic material reacts with calcium hydroxide liberated by the hydrating Portland Cement and forms cementitious compounds generally known as C-S-H gel. The reaction can be given as under:

The Portland Pozzolana Cement produces less heat of hydration and offers greater resistance to the attack of aggressive waters than normal Portland Cement. Moreover it reduces the leaching of calcium hydroxide liberated during the setting and hydration of cement.

The Portland Pozzolana Cement is ideally suited for the following construction. Hydraulic structures Mass concreting works Marine structures Masonry mortars and plastering Under aggressive conditions. All other application where OPC is used. The compressive strength of PPC as per BIS code at present is equivalent to that of 33 grade OPC. The major quantity of flyash based PPC in India Cements Limited is presently being produced at Sankarnagar and Sankari Works of India Cements Limited at Tamilnadu. However depending of the requirement of flyash based PPC could be produced at all the Plants of India Cements Limited in Tamilnadu and Andhra Pradesh. The PPC being manufactured by ‘India Cements Ltd’ meets the strength requirements of 53 grade. The physical and chemical requirement as per BIS are given in table below:

Physical Characteristica of PPC (BIS Requirements)

IS Code

Fineness (sq.m/kg) min

Soundness by

Setting time

Compressive strength

Lechatlier (mm) max

Auto clave Max (%)

Initial (mts) min

Final (mts) Max

1 day Min Mpa

3 day Min Mpa

7 day Min Mpa

28 day Min Mpa

(IS 269-1989)

225

10

0.8

30

600 Specified

NS

16

22

33

Chemical Characteristics of PPC (BIS Requirments)

IS Code

Lime Saturation Factor

Alumina ratio Min.

Insoluble Residue (%) Max.

MgO (%) Max.

Max. Sulphuric anhydride

Loss on Ignition (%) Max.

(IS 1489-1991) Part-I (flyash based)

Not Specified

Not Specified

X+4(100-x)/4

6

3% Max

5

X – Declared % of Flyash

Comparison of strength characteristics of PPC produced at HBL with that of BIS requirements can be seen in the figure below